Phenolic compounds classification and their distribution in winemaking by-products

The wine industry produces thousands of tons of residues, which represent a waste management issue, both ecologically and economically. The large amounts of grape by-products in winemaking process have been described as an important natural source of polyphenols with health promising properties. Phenolic compounds are found in winemaking by-products, including in seeds, skins, stems and pomace of grapes. Among the several classes of naturally occurring phenolic compounds flavonoids are one of the most important, being acknowledge with some biological properties, such as antioxidant, cardioprotective, antiproliferative, anticancer, anti-inflammatory, antiaging and antimicrobial, which has led to an interest both by industry and the scientific community. Circular economy concerns turned the focus to the presence of bioactive phenolic compounds in by-products, namely to those generated in the winemaking process. This review summarizes current knowledge and recent insights in the phenolic compounds found in the principal grape by-products: stems and pomace (seeds and skins).